Multistation microwave communication system



June 6, 1950 G. G. BRUCK ErAL 2,510,461

MULTIsTATIoN MICROWAVE COMMUNICATION SYSTEM VFiled April 9, 194s Patented June 6, `1:1950

MULTISTATION MICROWAVE COMIMUNICATION SYSTEM George VGr. BruckEast Orange, N. J., Robert M.

Sprague, Waban, Mass., and MalcolmC. Vosburgh, New York, N. Y., assignors to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application April 9, 1946, serial No, 660,596

This invention relates tov radiov communication systems, and more particularly' to the terminal stations' of a frequency-modulated radio communication system comprising, Vfor example, two widely separated terminal stations and a plurality' of intermediate relay'stations, all operating on diierent mean carrier frequencies, the system permitting two-way transmission of intelligence between any and all of the stations included therein, with the'carrier wave emanating from one of the terminal stations'and "from each intermediate relay station,v hereinafter referred to as the slave stationsvunder the controlu of the carrier wavereceived "at each such station, and all under the control of the carrier wave originating at the remaining terminal station, hereinafter referred to as the master station.

A communication'system having the foregoing characteristics is disclosed inthe copending application of George GL Bruck, Philip E. Volz, Paul J.4 PontecorvoV and Malcolm C. Vosburgh, entitled Radio communicationsystems, Ser. No. 650,716,

For example, itv o 14 Claims.' (Cl. 2250-13) mission because its transmitting and receiving v.

channels are not isolatedv from each other, as a result of which any intelligence originating 'at any given station in the system is heard at'that same station. Obviously, if said station is receiving intelligence at the same time that it is being 1 used for transmission, the 'incoming and outgoing signals mix, Vand both become unintelligible.

It is, therefore, the main object of the present invention to provide a communication system of the type above referred to in which the transmitting and receiving channels of feachvstation are so divorced from each other as to permit their simultaneous use without interference.

This, and other objects of the present invention, which will become more apparent as the detailed description thereof progresses, are attained, briefly, in the following manner:

Throughout the remainder of this specification it will beassumed that the system comprises merely two widely separated terminal stations, withno intermediate relay stations, and with one of said terminal stations functioning 4as a master, and the other as a slave. It is to be understood, however, that it is preferred that both terminal stations be so constructed as to be operable, at will, as either a master or a slave station.

At the master station, to a description of which this-specincation will lbe limited for the time being, a carrier wave, having a frequency, for eX- ample, of 10,000 mc./sec., is generated. There is also generated at said master station a subcarrier wave having a frequency, for example, of 50 mc./sec. Said sub-carrier wave is adapted to be frequency modulated in accordance'with local intelligence, land the resulting modulated subcarrier wave is mixed with a portion of the locally-'generated carrier wave to transfer thereto said local intelligence.

The output of the mixer, neglecting any intelligence for the moment, includes the carrierV wave, the usual upper sideband wave consisting of the carrier wave plus the sub-carrier wave, and o the usual lower sideband wave consisting of the carrier wave minus the sub-carrier wave.

Allof these waves 'are applied to an energytransmission system'` designed to divide each into oppositely-phased constituent waves of equal ampli'tudes. Said constituent waves are caused to suffrreflection by devices, one of which is tuned tothe frequency of one or the other of said sideband waves, having such relative reection coefncients that, upon recombination'of the reflected,

unattenuated portions thereof, a zero output results, provided said sideband waves have not deviated from their original frequencies.

ing anY amplitude which is a function of the magnitude of said deviation, and having a phase, relative to that of the initially applied sub-carrier wave, which is a function of the sense of said deviation.

AThe residual sub-carrier wave so recoveredV is V combined with a suitably phase-shifted portion of the initially applied sub-carrier wave tode rive therefrom a unidirectional output whose amoutput is developed merely as a result of random 'drift in the frequency of the locally-generated carrier wave, `and serves to stabilize the carrierwave generator. However, said unidirectional output also varies in response to any locally-genf erated intelligence, and its application to the car- `,Tier-wave generator, therefore, serves, also, to f re- Aquency modulate said generator, the resulting If there has been a deviation, a residual sub-carrier wave j is recovered, said residual sub-carrier wave hav-M frequency-modulated carrier wave being radiated into space.

In earlier portions of this specification, it was stated that one of the devices utilized to reflect the constituent Waves derived from the locallygenerated carrier' and si'deband Waves* was timed to the frequency of Oheoi said sideband Waves. Now, said device is so designed as to transmit therethrough some of the energy of the particular sideband wave to which it is tuned, and this transmitted energy serves as local-oscnlator energy for the heterodyne reception oi any signal coming into the station.

The incoming carrier Wave', which or may' not include remotely-generated intelligence, is'

applied to a nigh-Q circuit, tuned to the frequency of said incoming carrier wave, to reduce to a minimum, extraneous signals. The' output of circuit, and the transmitted local sideband Wave above referred to, are combined to derive from one, constituent waves of opposite phase, and from the other, constituent waves or' like phase'. All or these constituent waves are then combined to* derive therefrom an intermediate-frequency wave whose mean frequency is an arithmetic function of the frequencies oi' the incoming carrier' Wave and the local sideband wave producing the same. I

Said intermediate-frequencyv Wave is demodulated' to extract therefrom any remotely-generated intelligence ccntained therein and' inasmuch as the localsidebar'id Wave utilized in the productionof said intermediate-frequency' Wave may have included local intelligence, means are pro'- vided to remove the latter.

At the slave station, the equipment thusiar vde'- scribed is duplicated, except that the' locallygenerated carrier wave, preferably, is of a' different frequency than that generated' at the' master station. The station. slave carrier wave may have a frequency, for ez'iample, of 10,01] mc.-/sec. Also, if the tuned reflecting device of the master station is resonant to the upper sideband wave generated. thereat, it is preferred that, at the slave station, said tuned reflecting device be resonant to the lower sideband Wave.

Now, at the slave station, as at the master station, the carrier wave is locally' frequency stabilized. In order, however, that the mean. frequency of the intermediate-frequency wave derived at said slave station be maintained at a predetermined. constant, it is necessary that the frequency of the locally-generated carrier wave be locked in with the frequency of the carrier Wave generated at the master station. If the frequency of the carrier wave generated at the slave station is, in the rst instance, improper, the sidebarid wave entering into the production of the slave station intermediate-frequency wave will be such that the demodulationl of said intermediate-frequency wave will yield, in addition to the intelligence contained therein, a unidirectional component Whose amplitude and sense depend., respectively, on the magnitude and sense of the deviation of the mean frequency of said intermediatefrequency Wave from its correct mean frequency. This unidirectional component is separated from the intelligence recovered from the intermediatefrequency wave, and is applied to means for altering the resonant frequency of the tuned reflecting or sideband-transmitting device of the slave station until the resonant frequency of the latter is such that the mixing of its output with the carrier wave received from the mas-ter station produces the correct intermediate-frequency Cwave.

However, altering the resonant frequency ol' the slave station sideband-transmitting device changes the amplitude of the sideband wave renetted thereby; 'and this?, in tlnin', produces a resiciualA subecarrier wave,- as explamed above in the description of the master station, which so ret-unes the slave station carrier-wave generator that, when. the local carrier wave is combined Witrr the local sub-carrier Wave. one or' the resulting sideband waves has a frequency corresponding to the altered resonant frequency of said sideband-transmitting device.

order tov prevent hunting, a portion of the unidirectional' component, utilized, as above, to retune the si'deband-transmitting device, ls also applied to thefsub-carrier wave generator to alter its frequency in opposite sense tothe alteration of the frequency of the carrier-Wave generator.

While it is preferred that the master station include the additional equipment just described, the unidirectional component resulting from the demoduiation of the remotely-generated carrier wave received at said masterV station is n'ot fed back' to the local frequency lcontrolling apparatus.

In the accompanying specification there' shall be described', and in the annexed drawing shown, an illustrative embodiment of the terminal station of the present invention. Itis, however, to

vbe clearly understood that the present invention is not to be limited to the details herein shown and described for4 purposesof illustration only, inasmuch as changes therein may be made Without' the exercise of invention, and Within the true spirit and' scope of the claims hereto appended.

In said drawing, the single figure is` a partial block, partial schematic diagram of a terminal station assembled in accordance with the principles of the present invention.

Referring now more in detail to the aforesaid` illustrative embodiment of the present invention, with particular reference to the drawing illustrating the same, the numeral IU designates anv oscillator for gener-ating a carrier wave wh, preferably, in the microwave region of the electromagnetic spectrum, having a frequency, for example, of 10,000 Ind/sec. 'Ihe output of the oscillator I0 is applied to the side branch II of a wave-guide assembly f2, known as a magic T, said assembly including, in addition to the side branch II, yanother side branch I3 collinear with said first side branch, a so-called E arm I4 extending at right angles to said side branches f.

Il and I2. and a so-called H arm I5 extending at right angles' to both said side branches and from the junction I6, then bends downwardly, and is then twisted through an angle of As the energy travelling along the side branch Il from the oscillator Le reaches the common junction I 6, it splits, part travelling along the H arm I5 to a matched load Il which absorbs f, the same part leaking across the T and travelling along the side branch I3, and part travelling .Y

along the E arm le to an electromagnetic horn I 8 adapted to direction-ally radiate the same.. The horn I8 is also receptive, in the opposite direction, of a remotely-generated carrier wave w'h,

which may be frequency modulated with intelligence ws, and which emanates from another terminal station. As already indicated, the carrier wave w'n may have a frequency of 10,010 rnc/sec. A portion of the carrier wave wh travelling down the side branch I of the magic T I2 is diverted, through an iris le, into the E arm 20 of another magic T 2| which also includes side branches 22 and 23 and an H arm 24, all extending from a common junction 25.

The E arm 2@ has a non-linear impedance, for example, a crystal 26, disposed therein to which there is applied the output of an oscillator 2 adapted to generate a sub-carrier wave w1 having a frequency, for example, of 50 mc./sec. oscillator 2 is adapted to be frequency modulated in accordance With local intelligence wa applied thereto through a microphone 23 and an audiofrequency transformer 29, so that the crystal 26, in addition to its being excited by the carrier wave oh, is also excited by the sub-carrier wave w1,- and sideband waves mica. Therefore, there travels down the E arm 2li, toward the junction 25, a carrier wave wh, and sideband Waves ontwik/Awa l Where Ich@ represents local intelligence of small amplitude resulting from initiallyapplying said local intelligence to the oscillator Z1 in such phase, with respect to the phase of the intelligence incorporated in the carrier Wave which is radiated, as to oppose the latter.

-At the junction 25, each of the carrier and sideband Waves just reerred to split into .constituent Waves of opposite phase, the constituent waves of one phase travelling along the side branch 22, and` those of the opposite phase travelling along the side branch 23. The side branch 22 is terminated by an adjustable attenuating device 30, and the side branch is terminated by a high-Q resonant circuit, such as a cavity resonator si provided With an iris 32 through which energy may enter the saine.v Said cavity resonator 3| is--tuned to one .of the sideband waves produced as a result of mixing .the outputs of theoscillators iS and 2l, and for the purpose of this description, it will be assumed that saidcavity resonator.

is tuned to the upper sideband Wave wil-i-wl.

.The constituent Waves incident upon the attenuating device 3@ and the cavity resonator 3i become partially absorbed and partially reflected, and said attenuating device and cavity resonator are designed, respectively, to have such relative reflection coeiicients that, When the reflected portions of said constituent waves Vare subsequently recombined in a non-linear device, as will hereinafter be more fully described, a zero output results, providedthe frequencyof the incident upper sideband Wave corresponds to the frequency to which the cavity resonator 3| is tuned.

Al3y Way of illustration, assume IQtoY be the reflection coefiicient of the attenuating device 30, and ,1 to be the reflection coefficient of the cavity resonator 3l with respect to Waves having frequencies oiresonance. Then, at the junction 25 of the magic T 2i, the combined reflected portions of the constituent waves of the carrier wh will have the form: (lo-l-l) cos wht, and the',

The'

6 atr the junction 25 of the magic T 2|, the reflected portions of the constituent Waves of the upper sideband wil-l-wi will have the form: (Fr-Fc) cos (w114-wot, and When this recombined wave is mixed with the recombined carrier Wave, a

residual sub-carrier or modulation wave will` result having the form: (IO-l-l) (T0-F) cos wit.'

It has been stated that, for the resonance condition, that is, for the condition Where the frequency of one of the sideband waves resulting from the combination of the outputs of the osci1` lators l0 and 2l corresponds to the frequency to which the cavity resonator 3| is tuned, it is desired that the recombination or the reflected portions of all of the constituent waves produce a Zero output. ln other words, and considering only the amplitude factors of the Waves involved,l

frequency of the upper sideband Wave wn-I-wi' from the resonant frequency of the cavity resonator 3|, no output appears across the crystal 33. In the event, however, there is deviation, brought about either by random drift in the frequency of the oscillator l0, or locally applied intelligence, a residual sub-carrier or modulation wave is recovered across the crystal 33, the wave so recovered having an amplitude proportional to the magnitude of said frequency deviation, and a phase, relative to the phase of the initially appliedsub-carrier wave w1, which is a function of the sense of said frequency deviation.

The output of the crystal 33 is applied, through a broadband amplifier 3a, whose center frequency corresponds to the frequency of the sub-carrier Wave e1, to a differential-amplitude detector 35 to derive a unidirectional output having an amplitude and sense depending, respectively, on the magnitude and sense of the above referred to 5f) frequency deviations. The differential-amplitude detector 35 may be of the type described in detail in the copending application of George G. Bruck and Philip E. Volz, entitled Frequencystabilizing system, Ser. No. 647,008, led February l2, 1946, now Patent No. 2,486,001, dated October 25, 1949, and is receptive, together with The unidirectional output of the differentialamplitude detector is applied, through any appropriate control device 3l, to the oscillator I0 to alter the frequency of the carrier wave wh in response to the deviations heretofore referred to.`

Ifsaid deviations are merely random, they are compensated for, thereby stabilizing the frequency of the carrier wave, and if said devia- 7 tions are 'the `result of flocally-fgenerated intelligence, theycause `the carrier wave -whichls radiated to be -f-requency modulated in accordance with said intelligence.

Now the cavity resonator 3l, in additionto communicating with the vside branch 23 vof the magic T'2l through the iris 32, also communi- Cates -Withthe I-I arm 33 Yof a third "magic T '59 which `includes `side Ybranches $0 and 4l and-an E -arm ft2, all extending from a common ljunction 553'. This magic T functions as am-ixer, as vdescribed in detail in the copending applicationof George G. Bruck, enti'tledMixing apparatus, Ser. No. 652,628, led March 7, 1946, now Patent No. 2,468,166, dated April 26, 19219, to combine a local, fixed-frequency wave, namely, aportion of the sideband wave wh-i-wi transmitted .by the cavity resonator 3l with an incoming carrier wave fwh, remotely generated at a slave station, to derive an intermediate-frequency Wave Cwd whose mean frequency is an arithmetic function of the frequencies of said sideband and in- Acoming carrier waves, preferably, the difference '.therebetween. ,I

The E arm 42 communicates with an energy- 'transmitting cavity resonator 43 which is receptive, from the side branch i3 of the `magic T 12,015 Vthe incoming carrier wave wmW-hich may or vmay not include remotely-generated intelligence wfg, and that portion of the locally-generated carrier wave en leaking across `'the ""lff of said umag'ic T '12, The cavity resonator 43 is tuned to the Temotely-generated carrier wave wh `s o that 4energy of 'any other frequencies 'is greatly attenuated thereby.

'Theside-pranches it and al are terminated, respectively, by Inon-linear impedances, for :eX- ansie, 'crystarsise anus-e5, Said'crystals ybeing cp;- ps'ite'ly'disposed'with respect to 'each other, and cdrihectelin series throug'hja 'resistor'l V'and a source "41 'of direct'current. The conductors con'- necting said "crystals 'pass through insulators 48 to 5i, inclusive, the insulators '-djand 5|? being of such construction (not 'specifically Ishown) as tofpres'tcapacitances 52 and 53 between one side "o'f`each of said crystals andthe waveegui'de system itself, ,thelatter being'grounded'as shown. The crystals il and @l5 are further c'onnectedito provideparallel outputs to ground through a ca"- pacitor 5i and the primary winding 55 of an output transformer 5S having a secondarywinding 51. `The sourcel of direct current is for thefplirpose of operating the'crystals M fand l5 a't favorable 'points along 'their -characteristic curves, and thefseries circuit is for the purpose fpass'i'hg'equal currents Atlrirough said crystals toaslsiire their similar action even though both l5e `niisi`natched to the wave-guide system,

lssume, for the moment, that the electric vectrf` the remotely-generated carrier 'wave wn, travelling along the E arm d2 toward the-com'- mon l'junction 39', is pointing upwardly, Yand'further ass'u'meth'at the electric vector of the locallyproduced Vsideband wave wh+w1,travellin'galoh`g tlieI-I arm 38 Atoward the common junction 3l',*is pointing'to the right at said junction 39,. When the former reaches the junction 439', it splits into I`two constituent' waves, one, having its electric Vector pointing to Ythe right, travelling along *che sdebranch 4c toward "t'rleerystai 44, aid'the thenhaving its electric vector r`'pointing to thelyflg tavellingalong the side branch '41 t`w`ardfthe crystal A5. When the "latter reaches tneijunctiohjit, too, 'splits into two constit- `dlit:"v'vaes, one ttravelling toward the cyst'ald 8 and the other travelling toward the crystal 45. with'both-having their electric vectors DOjn'ting in the-same direction,-namely, to the right. Thus,- there -arr-ive's at the crystal l two constituent carrier Waves Whichare -in phase, and there arrives at the crystal 45 two constituent carrier waves which are out of phase. Therefore, there is produoedat the crystal 4, a beat-frequency waves, and whose phase may be considered posiference between the frequencies of its component waves,and whose 'phase may be considered positive because its'component waves are in phase; W-hile-atfthe crystal d5, there is produced a bea-tfrequency wave having the same frequency as said zfirst-named beat-frequency wave, and having a phase which may be considered negative because its component waves are vout of phase. Howevemafs -toeach other, the two beat-frequency waves thus obtained are in phase, and set -up equal voltages of like .polarity across the crystals. Inasmuch as parallel outputs are taken from these crystals, addition occurs, and a constant-amplitude, intermediate-frequency wave wdapp'e-arsacross the primary winding 55 of the transformer 56.

Through -the secondary Winding 57 of the transformer '56, this intermediate-frequency wave ad, vtogether with any remotely-generated intelligence wa, and any small amount of locally-generated intelligence wa which may have been contained in the locally-produced sideband wave wh-i-wi, is lapplied to a broadband intermediatefrequency amplifier 53 lWhose center frequency corresponds to the difference ad between the frequencies of the component waves producing the same. The output'o'f the ampliner 58, consisting of the difference frequency wd and any intelligence wa and wfa'originating, respectively, at the master and-slave stations, is applied to a frequency discriminator 59 whose center frequency, likewise, `corresponds to said difference frequency wd. The discriminator extracts any intelligence included inthe intermediate-frequency input applied theretdwhich intelligence is then conveyed, through an audio-frequency amplifier G, and an audio-'frequency transformer tl, to phones l62 or any automatic recording instrument. In order to remove 'anylocally-fgenerated intelligence wa from the input to xthe phones 62, a small amount of said locally-@generated intelligence wa may be applied, through va transformer 53 and a potentiometer 54, 'to a transformer 55 so connected 'into the output circuit of the station as to oppose the locally-generated `intelligence applied thereto through the ltransformeri6 l Thus, atthe'master station, a frequency-stabilized 'carrier `Wave wir containing locally-generated intelligence wa is produced, and any remotely*- generated'intelligence wa contained in an incoming carrier'wavewh'received at said stationfis'so prevented 'from 4mixing with said locally-generated intelligence ILas to enable lthe transmitting and recivingchanrils of the station to be `uti"- lize'd simultaneously.

Now, at the slavestation, it is desired *to "lock in "the locally-'generated carrier wave wh with the master'station'carrier `wave wh. For this purpo's'e, the output of the v'clis'criminator '155 is =ap' which 'blocks any vintelligence Acontained in said output, :but passes the unidirectional component thereof. If the'slave statioh'carrier Wave whis of the correct mean frequency to begin with, the rfea'n frequency Uf "the Yinterinadia'te-fi'equncy Wvewfa develcpl'd 'at Said slave station Will such that there will be no unidirectiona1 component coming from the discriminator 59, but should the mean frequency of said locally-generated carrier Wave be incorrect, there will be such a. component, and the magnitude and sense thereofv will be functions, respectively, of the magnitude and sense of the deviation of the mean frequency of said locally-generated carrier wave from its correct mean frequency.

In order to compensate for such a deviation, the output of the lter 61 is utilized to drive a servo-motor 68, mechanically connected, as shown by the broken line, to the local cavity resonator 3l, to retune the latter until its resonant frequency wh-w'i is such that when the sideband Wave transmitted by said cavity resonator to the local mixer 39 is combined with the incoming master station carrier wave wh, the mean frequency of the intermediate-frequency Wave wd will be such that it includes no unidirectional component.

As the slave station cavity resonator 3| is being so retuned, an output will be developed across the local crystal 33 for the reasons explained above in connection with the description of the master station, and said output will cause the local differential-amplitude detector 35 to also develop an output. The latter, being fed to the local frequency-control device 31, Will alter the mean frequency of the locally-generated carrier wave wh until the frequency of the lower sideband wave wn-wi, produced by mixing said carrier wave with the local sub-carrier wave w'i, corresponds tothe altered resonant frequency of the local cavity resonator 3|. Thus, there will always be a fixed relationship between the mean frequencies of the master and slave station carrier waves.

Because the servo-motor 68 will have inertia, hunting must be prevented, and for this purpose, a portion of the output of the filter 61 is applied toV any suitable frequency-controlling device 69 for adjusting the'frequency of the output of the local oscillator 21, this adjustment being such as to produce a sideband wave which actually halts the output of the discriminator 59 before the motor 68 has tuned the cavity resonator 3l to the correct frequency, the final tuning of said cavity resonator being the result of the coasting, rather than the positive driving, of said motor.

It is to be understood that it is intended that the master station also be provided with a switch 66, 'lter 6l, motor 68 and control device 69, but that at said station, the switch 66 be kept open. Thus, eitherstation can be used as a master or a slave.

This completes the description of the aforesaid illustrative embodimentv of the communication systems of the present invention, together with the mode of operation thereof. It willbe noted from all of the foregoing that the present invention'provides a system, having the characteristics set forth in the opening paragraphs of this specification, and permitting simultaneous transmission and reception at each of the stations therein.

Other objects and advantages of the present invention will readily occur to those skilled in the art to which the same relates.

What is claimed is:

/l. Apparatus for frequency stabilizing a carrier wave comprising: means, receptive of said carrier wave, for modulating the same to produce sideband waves; means, receptive of said carrier and sideband Waves, for deriving from each, op-

positely-phased constituent waves; means receptive of the constituent waves of one of said opposite phases, for partially attenuating and partially reflecting the same; means receptive of the constituent waves of the other of said opposite phases, for partially attenuating and partially reecting the same; said two last-named means having relative reflectioncoefcients at the frequency of one of said sideband waves equal, respectively, to Ic and 1/2 (Fe-l);I means receptive of the unattenuated, reflected portions of all of said constituent waves, for recombining the same and thereby reconstituting said carrier and sideband waves; means, receptive of said reconstituted carrier and sideband waves, for deriving therefrom oppositely-phased residual modulation waves; said oppositely-phased residual modulation waves being of equal amplitudes if the frequencies of said sideband waves remain constant, and of unequal amplitudes if said frequencies vary; means, receptive of said last-named residual modulation Waves, for deriving therefrom a final modulation wave Whose amplitude and phase depend, respectively, on the magnitude and sense of any such frequency deviations; means, receptive of said final modulation wave, for deriving therefrom a unidirectional output Whose amplitude and sense, likewise, depend, respectively, on the magnitude and sense of said frequency deviations; and means, receptive of said unidirectional output and coupled to the source of said carrier wave, for altering the frequency of said carrier wave in response to said unidirectional output.

2. Apparatus for frequency stabilizing a carrier wave comprising: means, receptive of said carrier wave, for modulating the same to produce sideband waves; a wave guide system including a first main branch, and a pair of auxiliary branches perpendicularly extending in opposite directions from a common junction with said rst main branch; said wave guide system being receptive of said carrier and sideband waves for deriving from. each, oppositely-phased constituent waves; means, having a reflection coefficient Ic at the frequency of one of said sideband Waves, and being disposed in one of the auxiliary branches of said wave guide system in the paths of the constituent waves of one of said opposite phases, for partially attenuating and partially reflecting the same; means, having a reflection coefficient lo equal to 1/2 (Fc-1), and being disposed in the other of the auxiliary branches of said Wave guide system in the paths of the constituent waves of thev other of said opposite phases, for partially attenuating and partially reflecting the same; said wave guide system including a second main branch extending from said common junction, mutually perpendicular to said first main branch and said auxiliary branches, and being receptive of the unattenuated, reflected portions of all of said constituent Waves for recombining the same and thereby reconstituting said carrier and sideband waves; means, receptive of said reconstituted carrier and sideband waves, forderiving therefrom oppositely-phased residual modulation waves; said oppositelyphased residual modulation waves being of equal amplitudes if the frequencies of said sideband waves remain constant, and of unequal amplitudes if said frequencies vary; means, receptive of said last-named residual modulation waves, for deriving therefrom a iinal modulation wave whose amplitude land phase depend, respectively, on the magnitude and sense of any such frelil (111611637 deviations? meal's; receptive' (iffy St'ld lafl modulation Wave-for derivingtherefrom a uni'- dir-ect'ionaloutputv Whose amplitude and sense, likewise; depend, respectively,- onl the-magnitude and-` sens'e off saidfrequency deviations; and means, receptive of' said3 unidirectional output and coupled to-'the s'ou'rce'- ofsai'd carrier Wave, for alteringthe frequency of: S'ai'd carrier wave inrespcnseto said unidirectional output.

3. Apparatus for frequency stabilizing a carrier WaveV comprisil'igl:` means, receptiveof said carrier' Wave, fori modulatirigthe` same: to -produce side band waves; a waveguide system including a first main branclL- and a"- pair' of auxiliary branches' perpendicular-ly' extending' inopposite directions f-'roma common junction withA said rst main branchsaid Wave" guide system beingreceptive of said carrier and' sideband waves for deriving from each, -oppositely-phase'dconstituent vvaves';` a cavity resonator', tuned to the frequency of one of said sideband Waves, having a reflection cce'nicient Peat theffrequency of said one of said sideband- Waves, and beingV disposed inxA one of theauxiliary branches of said wave guide system in thev paths ofl the constituent waves of one of said opposite phases; for partial- 1y -attenuating and partially' reflecting the same; a resistive i'mpe'dance, hav-ingl arelection coeicient-F equal tcl-V2.' (Fe-:1), and-being disposeddn the other of the auxiliary branchesof said wave guide system. in'- the paths o'ff the constituent Waves of the otherv of said'Y opposite phases', for partially attenuating-Y and partially reflecting.- the same; said Wave guide system including a second main-branch extending from saidcommon junction, mutually perpendicular to said first main branch and said auxiliary branches; and being receptive of the" unattenuat'ed, reflected portions of all of said constituent Waves for recombining theVr same and therebyreconstituting said carrier and sideband" Waves; meansreeeptive ofA said reconstituted carrier and. sideban'd' Waves, for deriving therefrom oppositely-phased residual modulation Waves; said: oppositely-phased residual` modulation'` waves. being of. equalA amplitudes' if the frequencies; of said! sideband` Waves remain constant aridi ofv unequal'l amplitudes if said; frequencies vary;- means, receptive of said last-named residualimodulation-Waves;for deriving therefrom a fllal modulationwave Whose amplitude and phasedepend', respectively, onthe magnitude and sensei of any suclifrequency dee viations; means, receptive of said-final modulationJ Wave, for deriving therefrom. a l'l'nidirectional output Whose amplitude and Sense, likewise, depend, respectively,-o'n the magnitude and se'nse of said frequency deviations; and means, receptive of said unidirectional output and coupledto' the sourcey o'f said carried Wave, for altering the frequency of said carrier-Wave in re spcnse'- to said unidirectional output.

4. Apparatus for frequency stabilizing a carrie'rwave comprising: means, receptive of said.- carrier Wave, for modulating'. the sarneto produce sideband Waves;- means, receptive of said carrier and sideb'and Waves-,- for-deriving'- from each, oppositely-phase constituent Waves`;-means, having a reflection coefficient Fe at the frequency of one of said? sidebandwaves, and being irltl-e'rp'osed in the paths of the constituent Waves of one of said opposite phases, for partially' atten-ua'ti-ngl and partially reflecting the saine; means, having a reflection` coeicient Fo equal to` 1/2 (-Ifeel'), and being interposed in the paths' ofthe constituent Waves of the other of4 'saldi opposite' phases; for

liz

partially attenuanngf and partially: reflecting-.fthe saine ;1 means, receptive o'fthe; unatten'uafed. ref flecte'd` portions o'f all of said consti-tuent Waves; for! recombiningtheY same and'l therebyrecon s'tituting saidl carrier and sideb'an'dlw-avesgmeans, receptiveA of saidl reconstitutedl carrier and sideband- Waves for deriving therefromoppositely# phased' residual m'odulation Waves;l said1 oppo'- sitely-phased residual r'nodulationl Waves being; of equal-amplitudes if the frequenciesof said sideba'iidl Wav-es remain constant, andi ofrunequall ani'.- plitudesl if said frequencies' vary.; means, recep tive off saidlast-named'. residuali modulation waves, for' deriving therefrom a finali modulaiti'on- Wave Whose amplitude and phase: depend; respective!y;` on.` th'el magnitude andi sense of any such frequency deviations: ai differential ampli'- tude detector, receptive. off a portion ofv thefinitialv modulating energy ami'. said nalf'modul'a'- tion Wave, for deriving therefrom. a.- un'idirectional output Whose amplitude and sense', like"- wi'se, depend.; respectively, Online magnitudeand sense of:` said frequency deviations; andi means@ receptive of.' saidl unidirectional. output and coupledto. the source oisa-iiiearrier wave, for altera ing the frequency-f ofs'aidcarrierwavein response to2 said unidirectionali output.

5. Apparatus` for frequency stabilizing ai cai@ ri'er Wave comprising-t. mealls,V receptive of Said carrier wave,.for'rnodulatin'g the sameto produce sidebandf Waves; ai wave guide system. including: a first main branch, andI a pair of' auxiliary branches perpendicularly? extending in: opposite directions from a common junction with saidrrst main branch; said Wave` guider system: being.; ree ceptive: of said' carrier. andi sideband waves for derivirigr from. each, oppositely'ephaseet` constitu ent Waves; means, having a reflectioncoecient Fc: atthefrequen'cy'of one of said: sidebandwaves, and'. being disposed inl onev ofV the,t auxiliary branches ofsaid. wave guide;- systeml in thepaths of the-constituent waves of: one ofi said-z opposite phases, for' partially attemiatirugi amd" partially reflecting the samer.' means, having a; reflection c'o'efcient F0 equa-l-V toA 1,/2 (lie-1f), andrbei'nfg dise posed-y i-n: the other of the: auxiliary branches of saidv'zave guide systeiir-V mthe paths of* the con stitue'n-t Waves: olf' the other of.' said opposite phases, for partially attenuating and partially reiiecting the-same; said' wave guide systemin, clu'ding. a secondi main branch entend-ing.l from said common junction; mutually perpendicular to1 said rst' main. branch and. said auxiliary branches,` and beingv receptive ofA theunattenu; ated; reflected portions of all: ofsa'id.' constitu ent waves for recombining the same and thereby reconstitutinglsaid. carrier and sideband waves; means, receptive of said reconstituted? carrier and. sideban'd' waves', for deriving therefrom opposit'elyl-pliasedl residual? modulation Waves. said oppo'sitelyf-phasedl residual: modulatitm.y waves beingV of. equa-l amplitudes? it' the frequencies; of said sidebandf Waves remain constant,` and:v of une equalv amplitudes ifi said. frequencies vary; means,A receptive: of saldi' last-namedi residual' mod-ula'-v tion waves, for deriving therefrom a finali-niedli-Y lati'on. Wave whose amplitude and.; phase depend, respectively, on the magnitude-andsenseof 'any such frequency deviations; a-.d'ilferential amplia tude detector, receptive of a portieri of the initial modulating energy-y and saidfin-ali` modulation Wave, for deriving therefrom a unidirectional output' Whose amplitudeand-sense, likewise, depend, respectively, ori-the magnitudeandi-sensed said-frequency deviationsg aafldmeans receptive of said unidirectional output and coupled to the source of said carrier wave, for altering the frequency of said carrier wave in response to said unidirectional output.

6. Apparatus for frequency stabilizing a carrier wave comprising: means, receptive of said carrier wave, for modulating the same to produce sideband waves; a wave guide system including a rst main branch, and a pair of auxiliary branches perpendicularly extending in opposite directions from a common junction with said rst main branch; said Wave guide system being receptive of said carrier and sideband Waves for deriving from each, oppositely-phased constituent Waves; a cavity resonator, tuned to the frequency of one of said sideband Waves, having a reflection coeflicient Ic at the frequency of one of said sidebandwaves, and being disposed in one of the auxiliary `branches of said wave guide system in the paths of the constituent Waves of one of said opposite phases, for partially attenuating and partially reecting the same; means, having a reiiection coefficient Io-equal to 1%; (Tc-1), and being disposed in the other of the auxiliary branches of said wave guide system in the paths of the constituent Waves of the other of Asaid opposite phases, for partially attenuating and partially reflecting the same; said Wave guide system including a second main branch extending from said common junction, mutually perpendicular to said rst main branch and said auxiliary branches, and being receptive of the unattenuated, reected portions of all of said constituent Waves for recombining the same and thereby reconstituting said carrier and sideband Waves; l means, receptive of said reconstituted carrier and sideband waves, for deriving therefromoppositely-phased residual modulation waves; said oppositely-phased residual modulation Waves being of equal amplitudes if the frequencies of said sideband waves remain constant, and of unequal amplitudes if said frequencies vary; means, receptive of said last-named residual modulation waves, forr deriving therefrom a final modulation wave Whose amplitude and phase depend, respectively, on the magnitude and sense of any such frequencydeviations; Ya differential amplitude detector, receptive of a portion of the initial modulating energy and lsaid final modulation Wave, for deriving therefrom a unidirectional output VWhose amplitude and sense,

likewise, depend, respectively, on the magnitude and sense of said frequency deviations; and means, receptive of said unidirectional output and coupled to the source of said carrier wave,

for altering the frequency of said carrier wave in response to said unidirectional output.

'7. In a terminal station for a radio communacation system: means for locally generating a sideband Waves, for deriving from each, oppositely-phased constituent waves; means, having a reflection coefflcient Ic at the frequency of one of said sideband Waves, and being interposed in l the paths of the constituent Waves of one of said opposite phases, for partially attenuating and partially reflecting the same; means, having al reflection coencient Io equal to 1/2 (Fc-1), and being interposed in the paths of the constituent waves of the other of said opposite phases, partially attenuating and partially reflecting the same; means, receptive of the unattenuated, re-

ected portions of all of said constituent waves, for recombinfing the same and thereby reconstituting said carrier and sideband Waves; means, receptive of said reconstituted carrier and sideband Waves, for deriving therefrom oppositelyphased residual modulation Waves; said oppositely-phased residual modulation waves being of equal amplitudes if the frequencies of .said sideband Waves remain constant, and of unequal amplitudes if said frequencies vary; means, receptive of said last-named residual modulation waves, for deriving therefrom a final modulation Wave whose amplitude and phase depend, respectively, on the magnitude and sense of any such frequency deviations; means, receptive of a portion of the initially modulated sub-carrier Wave and said final modulation Wave, for deriving therefrom a unidirectional output whose amplitude and sense, likewise, depend, respectively, on the magnitude and sense of said frequency deviations; and means, receptive of said unidirectional output and coupled to the source of said carrier Wave, for altering the frequency of said carrier wave in response to said unidirectional output.

8. In a terminal station for a radio communication system: means for locally generating a carrier wavemeans for locally generating a subcarrier Wave; means, coupled to said last-named means, for modulating said sub-Carrier Wave in accordance with local intelligence; means, receptive of said carrier and modulated sub-carrier waves, for combining the same to produce sideband Waves; a wave guide system including a first main branch, and a pair of auxiliary branches perpendicularly extending in opposite directions from a common junction with s-aid rst malin branch; said wave guide system being receptive of said carrier and sideband waves for deriving from each, oppositely-phased constituent Waves; means, having a reflection coefficient llc at the frequency of one of said sidebandwaves, and being ydisposed in one of the auxiliary branches of said Wave guide system in the paths of the constituent waves of one of said opposite phases, for partially attenuating and partially reecting the same; means, having a reflection coefficient Iu equal to 1/2 (Pc-1), and being disposed in the other of the auxiliary branches of said wave guide system in the paths of the constituent Waves of the other of said opposite phases, for partially attentuating and partially reflecting the same; said wave guide system including a second main branch extending from said common junction, mutually perpendicular to said rst main branch and said auxiliary branches, and being receptive of the unattenuated, reflected portions of all of said constituent Waves for recombining the same and thereby reconstituting said carrier and sideband Waves; means, receptive of saidreconstituted carrier and sideband waves, for deriving therefrom oppositely-phased residual modulation waves; said oppositely-phased residual modulation waves being of equal amplitudes if the frequencies of said sideband Waves remain constant, and of unequal amplitudes if said frequencies vary; means, receptive of said last-named residual modulation Waves, for deriving therefrom a final modulation wave Whose amplitude andv phase depend, respectively, on the magnitude andsense of any such frequency deviations; means. receptive of a portion of the initially modulated` 'sub-carrier wave and said final modulation wave,

for deriving therefrom a unidirectional output Whose amplitude and sense, likewise, depend, respectively, on the magnitude and sense of Said frequency deviations; and means, receptiveof said unidirectional output and coupled to the source of said carrier wave, for altering the freq-uency of said carrier wave in response to said unidirectional output.

9. In a terminal station for a radio communication system: means for locally generating a carrier wave; means for locally generating a subcarrier wave; means, coupled to said last-named means, for modulating said sub-carrier wave in accordance with local intelligence; means, receptive oi said carrier and modulated sub-carrier waves', for combining the same to produce sideband waves; a wave guide system including a first main branch, land a pair of auxiliary branches perpendicularly extending in opposite directions from a common junction with said first main branch;- said wavey guide system being receptive of said carrier and sideband Waves for deriving from each, oppositely-pha-sed constituent waves; a cavity resonator, tuned to the frequency of one of said sideband waves, having a reflection coeici'ent Ic at the frequencyv of said Aone of said sideband waves, and being disposed in one of the auxiliary branches of said wave guide system in the. paths of the constituent waves of one of said opposite phases, for partially attenuating and partially reflecting the same; a resistive impedance, having areilection coelcient' Io equal to 1/ (rc-ll, and being disposed in the other of the auxiliary branches of said wave guide system the paths of the constituent waves of thel other ci saldi opposite phases, forpartia-lly attenuating and partiallyreilecting thesame; said wave guide system including a second main branch extending from said common junction, mutually perpendicular to said first main branch and' said auxiliary branches, and being receptive of the unattenuated; reflected; portions of all of saidconstituent waves forrecom-bining the same and thereby reconstitutingsaid carrier and sideband waves; means, receptive oi said reconstituted carrier and sideband waves, for deriving therefrom oppositely-phlased residualV modulation Waves; said oppositely-phased residuall modulation waves being of equal amplitudes if the frequencies of said' sideband waves remain constant, and of unequal amplitudes if said frequencies vary; means, receptive ofsaid; last-named residual modulationwa-ves, for derivingl therefrom a finalmodiilationwave whose amplitudel andi phase depend, respectively. on the magnitude and sense of any such frequencyy deviations; means, receptiveof a portion of the initially modulated sub-carrier wave andI saidA finalE modulation wave, for deniying therefrom a unidirectional output whose amplitude and sense, likewise; depend', respectively; onv the magnitude; andi sense' of said frequency deviations; and means, receptive of said unidirectional output and coupled; to the sourceofsaid carrier Wave, for altering the frequency of said carrier wave in response to said unidirectional output'.

I: I-rr a terminalstation fora radio communicationl system: means for locally generating a carrier wave; means, receptive of said locallygenerated' carrier wave, for modulating, the same to`- produce upper and lower sideband waves; means, receptive of a portion of said carrier wave and saidsideband waves, and coupledI back to wave, for stabilizing the frequencies of said sideband waves; means for receiving a remotely-generated, frequency modulated carrier wave; means, receptive of one of said frequency-stabilized sideband waves and said remotely-generated, frequency-modulated carrier wave, for combining the same to produce a frequency-modulated, intermediate-frequency wave whose mean frequency corresponds to the difference between the frequency of said last-named, stabilized sideband wave and the mean frequency of said remotely-generated carrier wave; and means, receptive of said intermediate-frequency wave, for extracting the intelligence contained in the frequency modulation thereof.

11. In a terminal station for a radio communication system: means for locally generating a rcarrier wave; means for locally generating a subcarrier wave; means, receptive of said sub-carrier wave, for modulating the same in accordance with local intelligence; means, receptive of said locally-generated carrier wave and said modulated sub-carrier wave, for combining the same to produce upper and lower sideband waves; means, receptive of a portion of said carrier wave and said sideband waves, and coupled back to said means for locally generating said carrier wave, for stabilizing the frequencies of said sideband waves; means for receiving a remotelygenerated, frequency-modulated carriei1 waive; means, receptive of one Vof said frequency-stabilized sideband waves and said remotely-generated, frequency-modulated carrier wave, for cornbining the same to produce a frequency-modulated, intermediate-frequency wave whose mean frequency corresponds to the difference between the frequency of said last-named, stabilized sideband wave and the mean frequency of said remotely-Vgenerated carrier wave; means, receptive of said intermediate-frequency wave, for extracting the intelligence contained in the frequency modulation thereof; and means, coupled intermediate the source of local intelligence and said last-named means', for removing from the output of the latter the locally-generated portion thereof. Y

12. In a terminal station for a radio communication system: means for locally generating a carrier wave; means, receptive of said locallygenerated carrier wave, for modulating the same to produce upper and lower sideband waves: a wave guide system including a rst main branch, and a pair of auxiliary branches perpendicularly extending in opposite' directions from a common junction with said .first main branch; said Wave guide system being receptive of. a portion of said carrier wave and' said sideband waves for deriving from each, oppositely-phased constituent waves; a cavity resonator, tuned to the frequency of one of said sideband waves, having a reflection coeilicient Ic at the frequency of said one oi said sideband waves... and being disposed in one of the auxiliary branches of said wave guidev system in the paths of the constituent waves of one of said oppositeV phases, for partially attenuatingY and partially reflecting the same; a resistive impedance, having a reflection coefficient Pc equal to I/f (llc-1.) and being disposed in the other' of the. auxiliary branches of said Wave guide system in the paths oi the constituent waves of the other of said opposite phases, for partially attenuating and partially reflecting the same; said; wave guide system including a second main branch extending from. said common said5 means for' locally generating' said carrier 75' junction, mutually perpendicular to said rst main branch and said auxiliary branches, and being receptive of the unattenuated, reected portions of all of said constituent waves for recombining the same and thereby reconstituting said carrier and sideband waves; means, receptive of said reconstituted carrier and sideband waves, for deriving therefrom oppositely-phased residual modulation waves; said oppositely-phased residual modulation waves being of equal amplitudes if the frequencies ofrsaid sideband waves remain constant, and of unequal amplitudes if said frequencies vary; means, receptive of said last-named residual modulation waves, for deriving therefrom a final modulation wave whose amplitude and phase depend, respectively, on the magnitude and sense of any such frequency deviations; means, receptive of said final modulation wave, for deriving therefrom a unidirectional output Whose amplitude and sense, likewise, depend, respectively, on the magnitude and sense of said frequency deviations; means receptive of said unidirectional output and coupled to the source of said locally-generated carrier wave, for stabilizing the frequency thereof in response to said unidirectional output; said cavity resonator transmitting therethrough a portion of the sideband wave to which it is resonant and which is incident thereon as aforesaid; means for receiving a remotely-generated, frequency-modulated carrier wave; means, receptive of said resonator-transmitted, frequency-stabilized sideband wave and said remotely-generated, frequency-modulated carrier wave, for combining the same to produce a frequency-modulated, intermediate-frequency wave whose mean frequency corresponds to the difference between the frequency of said last-named, stabilized sideband wave and the mean frequency of said remotelygenerated carrier wave; and means, receptive of said intermediate-frequency wave, for extracting the intelligence contained in the frequency modulation thereof.

13. In a terminal station for a radio communication system: means for locally generating a carrier wave; means, receptive of said locallygenerated carrier wave, for modulating the same to produce upper and lower sideband waves; means for receiving a remotely-generated, frequency-stabilized carrier wave; means, receptive of one of said sideband waves and said remotely generated, frequency-modulated carrier wave, for combining the same to produce a frequency-modulated, intermediate frequency wave whose mean frequency is an arithmetic function of the frequencies of said last-named sideband wave and the mean frequency of said remotely-generated carrier Wave; means, receptive of said intermediate-frequency wave, for deriving therefrom a unidirectional output whose amplitude and sense are functions of the magnitude and sense of any deviation of the frequency of said Vintermediate-frequency wave from a predetermined frequency; and means, receptive of said unidirectional output and coupled to said means for locally generating said carrier wave, for controlling the frequency of said last-named sideband Wave whereby the frequency of said intermediate-frequency Wave always corresponds to said predetermined frequency.

14. In a terminal station for a radio communication system: means for locally generating a carrier wave; means, receptive of said locallygenerated carrier wave, for modulating the same to produce upper and lower sideband waves; a cavity resonator, tuned to the frequency of one ofY said sideband waves and adapted to transmit therethrough a portion of said one of said sideband waves; means for receiving a remotelygenerated, frequency-stabilized carrier wave; means, receptive of said resonator-transmitted sideband wave and said remotely-generated, frequency-modulated carrier wave, for combining the same to produce a frequency-modulated, intermediate-frequency Wave whose mean frequency is an arithmetic function of the frequencies of said last-named sideband wave and the mean frequency of said remotely-generated carrier wave; means, receptive of said intermediate-frequency Wave, for deriving therefrom a unidirectional output whose amplitude and sense are functions of the magnitude and sense of any deviation of the frequency of said intermediatefrequency wave from a predetermined frequency; and means, receptive of said unidirectional output and coupled to said means for locally generating said carrier wave and said cavity resonator, for tuning said carrier wave generator and said cavity resonator whereby said resonatortransmitted sideband wave is such that the frequency ofsaid intermediate-frequency wave a1- ways corresponds to said predetermined frequency.

GEORGE G. BRUCK. ROBERT M. SPRAGUE. MALCOLM C. VOSBU'RGH.

REFERENCES CITED The following references are of record in the file of this patent:

UNTTED STATES PATENTS Number Name Date Re. 21,955 Chaiee Nov. 25, 1941 1,921,168 Royden Aug. 8, 1933 2,114,036 Smith et al Apr. 12, 1938 2,289,444 Mayr July 14, 1942 2,317,547 McRae Apr. 27, 1943 2,379,395 Ziegler et al June 26, 1945 2,380,288 Bligh et al July 10, 1945 2,402,606 Davis June 25, 1946 2,408,791 Magnuski Oct. 8, 1946 2,419,527 Bartelink Apr. 29, 1947 2,424,796 Carlson July 29, 1947 Certificate of Correction Patent No. 2,510,461 June 6, 1950 GEORGE G. BRUCK ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 3, line 33, for "intermediate-frequency read intermediate-frequency; line 40, for the Words station slave read slave station; column 8, line 9, strike out Waves, and Whose phase may be considered posi and insert instead were lwhose frequency corresponds to the dif; column 10, line 10, after means insert a comma; column 11, line 59, for carried read carrier; line 73, for (F-1)read (I-1); column 16, line 68, for To, rst occurrence, read To; column 17, line 21, after means insert a comma; lines 50 and 51, for remotely generated read remotelygenerated; line 53, after the syllable ulated strike out the period and insert instead a comma;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the oase in the Patent Oce.

Signed and sealed this 5th day of September, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assistant Commissioner of Paten'ts. 

